The present invention relates generally to sensing devices for use in connection with apparatus for indicating the load sustained by the lines, cable and the like in cranes, derricks, and similar equipment.
Heretofore, apparatus for indicating load forces has, in the main, been so designed as to provide a pair of load reaction arms arranged to move either towards each other or away from each other under the application of the load forces. For a number of years, it has been common practice to utilize sensing devices of the hydraulic load cell type which could be readily mounted between the load reaction arms of the apparatus. The hydraulic load cell device was in one case arranged mechanically to subject the load cell to compression forces when connected between the load reactive arms of the apparatus which were movable away from each other under the load forces, and in the other case was designed to subject the hydraulic load cell to compression forces when the load reaction arms were moved towards each other. Also, in a similar manner load sensing devices utilizing electronic or electric load cells have been known heretofore.
More recently, as disclosed in U.S. Pat. No. 3,999,427 dated Dec. 28, 1976, it has been known to utilize a hydraulic-electronic load sensing unit having a pair of operatively associated load cells, one of the cells being of the hydraulic type and the other of the electronic type. The unit of this patent, however, is limited in use to load indicating apparatus in which the load reaction arms are movable towards each other under the applied load forces.
It is the purpose of the present invention to provide a hydraulic-electronic load sensing device which is susceptible of use for load sensing apparatus in which the load reaction arms move away from each other under the applied load forces.
In the load sensing unit of the above mentioned patent, selective use of the load cells is accomplished by selectively by-passing the load forces acting on one or the other of the load cells by means of a mechanical expedient in order to use one or the other of the load cells as the active load sensing medium of the unit. In the present invention, the by-passing means for the load forces applied to the hydraulic load cell has been greatly simplified, and the load by-passing mechanical means for the electronic load cell has been eliminated and replaced by a simplified arrangement which permits electrical disconnection of the indicator from the electronic cell, without the necessity of having to alter its responsive action to the load forces.